Organo-metallic titanium catalysts for the preparation of polyesters



United States Patent ORGANO-METALLIC TITANIUM CATALYSTS FUR THEPREPARATION OF POLYESTERS John R. Caldwell, Kingsport, Tenm, assignor toEastman Kodak Company, Rochester, N. Y., a corporation of New Jersey NoDrawing. Application October 3, 1952, Serial No. 313,072

13 Claims. Cl. 260-75) This invention relates to a process for preparingpolyesters which comprises condensing a diester of a dicarboxylic acidwith a polyhydroxy compound in the presence of at least one of a groupof novel catalytic condensing agents which are alkali metal and alkalineearth metal salts containing a complex titanium hexalkoxide radical andwhich are defined hereinbelow. These novel catalytic condensing agentscan be advantageously employed in the preparation of linear polyesterswherein the dicarboxylic acid is an aromatic compound. which does notcontain any ethylenic (olefinic) unsaturation and the polyhydroxycompound is a dihydroxy compound. In preparing such linear polyesters itis advantageous to conduct the condensation in an inert atmosphere at anelevated temperature which is increased during the course of thecondensation up to a temperature of from about 225 to about 310 C., thecondensation being conducted during the latter stages thereof at a verylow subatmospheric pressure. p

This application contains subject matter disclosed to some extent in acopending application, Serial No. 143,594, filed February 10, 1950, byJ. R. Caldwell, now U. S. Patent No. 2,614,120, dated October 14, 1952.This application also contains subject mater disclosed in othercopending applications filed on even date herewith by J. R. Caldwell,Serial Nos. 313,061 through 313,071.

Various polyesters of dicarboxylic acids and polyhydroxy compounds arewell known in the prior art and have been used, for example, in themanufacture of paints and varnishes. Moreover, prior art disclosures setforth various linear condensation polyesters derived from dihydroxycompounds and dibasic acids such as terephthalic acid which are capableof being drawn into fibers showing by characteristic X-ray patterns,orientation along the fiber axis. However, many of these linearpolyesters possess a relatively low melting point and a fairlyconsiderable solubility in various solvents whereby they are ofrestricted utility, especially in the textile field. These polyestersvary considerably in their characteristics, depending on the particulardicarboxylic acid and the particular polyhydroxy compound employed.Generally speaking, these polyesters have various physicalcharacteristics which are not as satisfactory as could be desired.

The preparation of polyesters is well known in the prior art andinvolves the reaction of a dibasic dicarboxylic acid with a dihydric orpolyhydric alcohol. It is advantageous to employ esters of thedicarboxylic acid whereby ester interchange takes place with the glycolor polyhydric alcohol to form a polyester and an alcohol. When using theester interchange method, the time required to form the polyesters isgenerally considerably less than when the free dicarboxylic acid isemployed. The long chain in the polyester is built up by a series ofester interchange reactions wherein the glycol displaces a relativelylow-boiling alcohol component of the acid ester to form a glycol ester.During the last stages of 2,720,502 Patented Oct. 11, 1955 the reaction,it is generally desirable to heat the condensing reaction mixture to atemperature of about 225 -275 C. or higher in order to maintain thefluid state. For this reason, the properties of the catalytic condensingagent are very important.

A desirable catalytic condensing agent must be active enough to promoteester interchange at a temperature below the boiling point of the glycolor other polyhydric alcohol. At the same time, the catalyst must bestable at temperatures of 225-310 C. or even higher is necessary.Furthermore, the catalyst must not cause decomposition or degradation ofthe polyester at these high temperatures.

In accordance with this invention, it has been found that certaincompounds are especially valuable for use as catalytic condensing agentsin the preparation of high melting linear polyesters. They have thegeneral formula structures set forth below:

wherein M is an alkali metal, e. g. lithium, sodium, or potassium, M isan alkaline earth metal such as Mg, Ca or Sr, and R is an alkyl radicalcontaining from 1 to 6 carbon atoms; R can be derived from a loweraliphatic alcohol such as methyl, ethyl, propyl, n-butyl, isobutyl,n-amyl, etc.

These novel catalysts can be advantageously employed in processes forpreparing polyesters, which processes are described below. These novelcatalysts are effective only when substantially anhydrous conditions areemployed and no free acid is present to a sufliciently significantextent to destroy the catalyst compound; thus, when free acids areemployed the acids are first reacted with a hydroxy compound (preferablythe polyhydroxy compound to be employed in the polyesterificationprocess) before the novel catalyst of this invention is added.

The novel bimetallic aldoxide catalysts can be made as described byMeerwein, Ann. 455, 227 (1927); 476, 113 (1929), viz. titaniumtetrachloride: is treated with sodium alkoxide to give Ti(OR)4 in excessalcohol; the alkali metal or alkaline earth metal is then dissolved inthe alcohol solution. Alternatively, a solution of titanium alkoxide canbe mixed with a solution of the alkali metal or alkaline earth metalalkoxide in the calculated proportions.

As shown by Meerwein, these catalysts are not merely mixtures of the twometallic alkoxides. They are definite compounds having a salt-likestructure. The titanium alkoxide coordinates 2 mols of alcohol to forman acid having the structure:

Ti(OR)4+2ROH- (Ti(OR)s)- -'+2H+ This acid can then be reacted with asuitable alkali metal, alkaline earth metal, an alkoxide thereof, e. g.sodium alkoxide, to give an acid salt having the structure:

H2(Ti(OR)s+NaOR NaH(Ti(OR)e)-IROH The acid salt can react with anothermol of alkali metal alkoxide to form a neutral salt according to theequation: NaH(Ti(OR)e) +NaOR- Na2(Ti(OR)s) +ROI-I These salts are muchmore efiective as catalysts than either of the metal alkoxides usedalone. Although the neutral salt, containing 2 atoms of alkali metal, isan eflicient catalyst, the acid salt is usually to be preferred becauseit tends to be more stable under the conditions of the reaction.

The novel catalysts of this invention give a very rapid reaction rate atall stages of the polyesterification process, including the final stepwhere the molecular weight is built up. They are particularly valuablefor the preparation of high melting polyesters from 1,6-hexanediol and1,5-pentanediol. It is well known that these glycols have a tendency todecompose at temperatures above 250-260 C. and hence are difficult touse. With the novel catalysts described above polyester reactionsemploying these glycols can be carried out at temperatures up to 300 C.or even higher without excessive decomposition.

The novel catalysts can, in general, be employed for the preparation ofsubstantially all polyesters involving an ester interchange reactionbetween a dicarboxylic acid ester and a glycol or glycol ester. Thecatalysts are especially valuable for the preparation of polyesters thatmelt above about 240 C., as for example, polyethylene terephthalate. Theprocess of the invention is applicable to all of the polyestersdescribed herein.

By employing the novel catalysts of this invention the reaction rate ofthe polyesterification process can be increased by a factor which isgenerally from about 2 to 5 times the reaction rate obtainable whencatalysts known in the prior art are employed. Moreover, the novelcatalysts of this invention have the valuable characteristic ofminimizing side reactions which have the tendency of causingconsiderable degradation of the polyester products at the relativelyhigh temperatures employed in preparing highly polymeric polyesters.Furthermore, by employing these novel catalysts to increase the rate ofcondensation, the time available for possible decomposition of the highmolecular weight polyester molecules being formed at high temperaturesis appreciably reduced. Thus, by increasing the reaction rate, the timerequired to make a polyester is reduced which is quite important becauseat 250-300 C. the degree of color formation and extent of deleteriousside reactions is proportional to the time of heating.

The polyesters produced when employing these novel catalysts havegreatly improved properties as compared to products obtained employingcatalysts known in the prior art. The molecular weight is considerablyhigher whereby highly polymeric polyesters are obtained. The color ofthe polyesters obtained is excellent; the products can therefore beemployed for purposes calling for white or colorless materials. Thephysical properties of the polyesters obtained are also superior. Athigh temperatures there is a great improvement in the inherentviscosities of linear polyesters which are suitable for melt spinning orextrusion whereby fibers, films, etc. can be produced having propertiessuperior to those obtainable with known catalysts.

The herein described novel catalysts are especially valuable for thepreparation of polyesters employing diesters of p,p'sulfonyl dibenzoicacid as described in copending applications filed on even date herewithby J. R. Caldwell, Serial Nos. 313,061-313,068. Many of these polyestersare very high melting and the reaction must often be carried out at atemperature of 280-300 C. or higher. It has been found that relativelyfew catalysts are effective at this temperature other than thosedescribed in this application.

It is an object of this invention to provide new and improved catalyticcondensing agents for promoting the formation of improved polyesters inprocesses involving ester interchange and alcoholysis. A further objectof this invention is to provide a new and improved method for thepreparation of polyesters wherein such new and improved catalysts areemployed. Other objects will become apparent elsewhere in thisspecification.

A broad aspect of this invention relates to a process for preparing apolyester which comprises condensing under substantially anhydrousconditions at an elevated temperature in an inert atmosphere a diesterof a dicarboxylic acid with from about 1 to about equivalent proportionsof a polyhydroxy compound, in the presence of a catalytic condensingagent selected from the group consisting of those compounds having theformulas: 1

MH(Ti(OR)s) M2(Ti(OR)6) M(HTi(OR)e)2 and M'(Ti(OR)s) wherein R1 and R4each represents a substituent selected from the group consisting of analkyl radical containing from 1 to 10 carbon atoms and anomega-hydroxyalkyl radical containing from 2 to 12 carbon atoms, R2 andR3 each represents (CH2)1I1 wherein n is a positive integer of from 1to' 5 inclusive and X represents a divalent aromatic radical selectedfrom the group hav-' ing the following formulas:

wherein Y represents a divalent radical selected from the groupconsisting of and ((fiHzM-r-CHa N wherein m is a positive integer offrom 1 to 5 inclusive, (B) with an alpha, omega-dioxy compound selectedfrom the group consisting of those compounds having the followingformulas:

and

R5-O-(CHZ)pO-R6 and R5O- (-R'z-O) qR'lOR6 wherein p represents apositive integer of from 2 to 12 inclusive, R5 and Rs each represents asubstituent selected from the group consisting of a hydrogen atom and anacyl radical containing from 2 to 4 carbon atoms, R7 represents analkylene radical containing from 2 to 4 carbon atoms and q represents apositive integer of from 1 to 10 inclusive, the alpha, omega-dioxycompound being employed in such a proportion that there' is at least anequivalent amount of alpha and omega oxy substituents in proportion tothe carbalkoxy substituents in the overall combination of the aromaticdiesters and the alpha, omega-dioxy compounds, (C) in the presence of acondensing agent selected from the group consisting of the novelcatalysts set forth above, (D) at an elevated temperature which isincreased gradually durof from about 225 to about 310 C., (E) thecondensation beingconducted in an inert atmosphere, (F) and conductingthe condensation at a very low pressure of the inert atmosphere duringthe latter part of the condensation.

Advantageously, the condensing agent is employed in an amount of fromabout 0.005% to about 0.2% based on the weight of the aromaticdicarboxylic acid diester. Higher and lower proportions can also beemployed".

Advantageously, the alpha, omega-dioxy compound is employed in such aproportion that there are from about 1.2 to about 3 alpha or omega oxysubstituents in proportion to the carbalkoxy substituents in the overallcombination of the aromatic diesters and the alpha, omega dioxycompounds. Higher and lower proportions can also be employed.

Since the alpha, omegadioxy compounds which can be employed inaccordance with this invention are most advantageously alpha, omegadihydroxy compounds and in order to facilitate the phraseology which isemployed in this specification, such compounds-will hereinafter bereferred to as polyhydroxy or dihydroxy compounds although it is to beunderstood that the alpha, omegadioxy compounds of the type describedabove are in tended to be coveredby the term dihydroxy compounds or theterm polyhydroxy compounds as such terms are employed herein.

Advantageously, the temperature employed during the earlier part of thecondensation is from about 150 to about 220 C. Higher and lowertemperatures can also be employed.

Advantageously, the low pressure defined under (F) is less than about 15mm. of Hg pressure (preferably less than 5 him). However, somewhathigher pressures can also be employed.

Most advantageously, the aromatic dicarboxylic acid diester is a diesterof p,p-sulfonyl dibenzoic acid or terephthalic acid and the polyhydroxycompound is a polymethylene glycol.

This invention also includesprocesses as described above wherebypolyesters can be prepared by replacing a part of the described aromaticdibasic acid diester with an ester of a replacement acid which can be analiphatic dibasic acid, e. g. carbonic acid, oxalic acid, succinic acid,adipic acid, sebacic acid, a,a-dimethylglutaric acid, diinethylmalonicacid, diglycollic acid, ,3-oxydipropionic acid, "y-oxydibutyric acid,maleic acid, fumaric acid, itaconic acid, etc. Similarly, otheresterified acidic modifiers can also be incorporated in conjunction withor in lieu of these replacement acid esters, e. g. linoleic acid,linolenic acid, fatty acids of linseed oil, soybean oil, cottenseecloil, tung oil, etc. The proc ess described above for the generalpractice of this invention need not be appreciably modified when suchpartial replacement acid esters are employed in conjunction with thearomatic dibasic acid esters except when they are unsaturated and tendto form insoluble and infusible products due to cross-linkage eiiects,in which event the process described hereinabove is advantageouslyterminated at an intermediate temperature of about 250 C. before thepressure is reduced whereby products are obtained which can be calledsoluble intermediate polyesters which are useful in preparing protectivecoatings. The various polyesters containing replacement acid esters asdescribed in this paragraph can be prepared according to proceduressimilar to those described in copending applications filed on even dateherewith by J. R. Caldwell, Serial Nos. 313,062 through 313,066.

Polyesters can also be prepared in accordance with this invention byreplacing a part of thedescribed dihydroxy compound with what can becalled a polyhydroxy compound which contains 3 or more hydroxy radicals,e. g. glycerol, sorbitol, pentaerythritol, di'pentaerythritol, fimethylglycerol, 2 methyl 2(hydroxymethyl) 1,3- propanediol,1,2,4-trihydroxybutane, etc. In the preparation of polyesters employingthese polyhydroxy compounds, the reaction mixture is not generallyheated to the high temperatures under reduced pressure as describedhereinabove since the product would become insoluble and infusible dueto cross-linking of the molecules; hence, the process is halted at about250 C. or less prior to the reduction in pressure of the inertatmosphere. Various solutions can then be prepared from theseintermediate polyester products which can then be cast into films orotherwise used in protective coating compositions. In preparing suchintermediate polyester products it is generally advantageous to employan unsaturated aliphatic dibasic acid diester in lieu of a part of thedescribed aromatic dibasic acid diesters, e. g. maleic, fumaric anditaconic diesters. The various polyesters containing replacementpolyhydroxy compounds as described in this paragraph can be preparedaccording to procedures similar to those described in a copendingapplication filed on even date herewith by J. R. Caldwell, Serial No.313,069.

The dihydoXy or polyhydroxy compounds defined above may not actuallycontain any free hydroxy radicals since they may be in esterified formas indicated by the formulas of the dihydroxy compounds set forth above.However, these hydroxy or substituted hydroxy radicals are referred togenerally as hydroxy radicals or substituents. Each diester isconsidered as containing two carbalkoxy radicals as that term isemployed in the definition of the process as described above since R1and R4 may be alkyl radicals, or omega-hydroxyalkyl radicals. Even whenthe process is preceded by the preliminary step described belowemploying free acids, the term carbalkoxy radicals in the description ofthe process is intended to encompass such free carboXy radicals. 7

Furthermore, this invention covers processes as defined above whereinthe aromatic dicarboxylic acid diester is formed by a preliminary stepcomprising condensing an aromatic dicarboxylic acid having the formula:

(wherein Ra, R3 and X are defined under (A) in the abovedescribedprocess), with a polyhydroxy compound which is defined above under (B)and is employed in the proportionsset forth under (B), at an elevatedtemperature, after which preliminary step the novel catalytic condensingagent which is defined under (C) is added and the. condensation iscompleted as defined under (D), (E) and (F). Advantageously, theelevated temperature employed during the preliminary step issubstantially that at which reflux conditions subsist; however, higherand lower temperatures can also be used. Advantageously, as indicatedhereinbefore, the polyhdroxy compound is employed in such a proportionthat there are from about 1.2 to about 3 hydroxy substituents inproportion. to the acid substituents in the overall combination of thearomatic diester and the polyhydroxy compound.

In preparing polyesters, especially linear highly polymeric polyesters,it is important to exclude oxygen and moisture at all stages of thecondensation, particularly during the latter stages thereof. An inertatmosphere can beemployed to excludeoxygen, e. g. it is advantageous toemploy a hydrogen or a nitrogen atmosphere. The reacting materialsemployed in the condensation are adr' vantageously' substantiallyanhydrous; however, if water is initially present or is formed duringthe course of the condensation, it can be substantially completelyremoved prior to the final stages of the condensation by operating inaccordance with the specified process. 1

Examples of aromatic dica'rboxylic acid diesters which can be employedas defined above under. (A) include the B-hydroxy-ethyl diester ofp,p'-sulfonyl dibenzoic acid, p,p'-sulfonyl dibenzoic acid dibutylester, m,p'-sulfonyl dibenzoic acid dipropyl ester, m,m-sulfonyldibenz'oic acid dihexyl ester, methyl terephthalate, hexylterephthalate,

isopropyl terephthalate, as well as various esters having the followingformulas:

CHaO-OC COOOHz Gino-o o o -0 02m 031110-0 o-OO OO-C o-o c3111 Thedihydroxy compounds which can be employed to form highly polymericlinear polyesters are straight-chain alkane diols, viz. polymethyleneglycols, wherein the hydroxy radicals are positioned at the two ends ofthe alkylene chain Examples of such glycols include ethylene glycol,1,3-propylene glycol, 1,4-butylene glycol, 1,6-hexylene glycol,1,10-decamethylene glycol, 1,12- dodecamethylene glycol, etc. Asindicated above, mono or diesters of these glycols can also be employed.Thus, the acetates, propionates and butyrates are examples of suchesters. The defined ether glycols can be employed either in lieu of thepolymethylene glycols or in conjunc tion therewith as modifiers.Examples of ether glycols include diethylene glycol, triethylene glycol,tetraethylene glycol, bis (4-hydroxybutyl) ether, bis (3-hydroxypropyl)ether, etc.

Valuable fibers can be advantageously prepared employing the highermelting polyesters which can be pro- HO-(CHzhfd-OC CsH10-OC CHaO-OCOHsO-O C- duced according to the procedures described herein. Preferablyno aliphatic ether glycol is employed when fibers are to be prepared.Furthermore, the aromatic acid diesters should ordinarily contain onlyp,p' linkages when highly polymeric linear polyesters are desired.However, on the other hand, valuable poleysters can be preparedemploying aliphatic ether glycols without any alkylene glycol althoughthe product obtained will not be suitable for forming useful fibers. Thesame applies to the employment of aromatic diesters containing linkagesin other than the para positions.

The catalytic condensing agents which can be employed have beendescribed above. From about 0.005% to about 0.2% of such catalysts basedon the weight of the diesters being condensed can be employed. Higher orlower percentages can also be employed. Generally, from about 0.01% toabout 0.06% of the catalyst condensing agent can be advantageouslyemployed based on the weight of the various diesters being condensed.

The temperature at whcih polyesterification can be conducted isdependent upon the specific reactants involved in any given reaction. Ingeneral, the reaction mixture can be heated with agitation at from about150 to about 220 C. for from approximately one to three hours in aninert atmosphere (e. g. nitrogen or hydrogen); the mixture can then beheated with agitation at from about 225-240 to about 280-310 C. in thesame atmosphere for approximately 1 to 2 hours. Finally, the pressurecan be greatly reduced to form a vacuum (less than about 15 mm. of Hgpressure but preferably on the order of less than 5 mm. of Hg. pressure)while the temperature is maintained in the same range (2253l0 C.) theseconditions are advantageously maintained for approximately 1 to 6additional hours. This final phase is advantageously carried out withgood agitation under the high vacuum in order to facilitate the escapeof volatile products from the highly viscous melt. The conditions can bevaried considerably depending upon the degree of polyesterificationdesired, the ultimate properties sought, the stability of the polyesterbeing produced, and the use for which the product is intended.

The employment of the novel catalytic condensing agents results inbetter products being prepared in much less time than is possible whenthe catalysts of the prior art are employed.

The reaction can be carried out in the presence or absence of a solvent.Inert, high boiling compounds, such as diphenyl ether, diphenyl, mixedtolyl sulfones, chlorinated naphthalene, chlorinated diphenyl, dimethylsulfolane, etc., can be used as the reaction medium.

It is important to exclude oxygen and moisture at all stages of thecondensation reaction. Inert atmospheres which can be advantageouslyemployed include nitrogen, hydrogen, helium, etc. Good agitation isprovided during the polyesterification process. Substantially anhydrousreactants can be advantageously employed although this is not essential,especially if any water is removed in the earlier stages of thecondensation.

In the examples given below, the hot bar sticking temperature isreferred to in several instances. The hot bar sticking test can bebriefly described as follows: A polyester fiber is placed on the flatsurface of a heated bar and a weight of grams is applied to the fiberalong a distance of inch of the fiber length. The contact surface ofthis weight has a coating of polytetrafiuoroethylene which acts as athermal insulator. The fiber is allowed to remain in contact with thebar under this weight for one minute. The minimum temperature at whichthe fiber adheres to the hot bar under these conditions is the stickingtemperature as that term is employed in the examples given herein.

This invention can be further illustrated by the following examples; inaddition to these examples it is apparent that other variations andmodifications thereof can be adapted to obtain similar results.

9 Example I.-NaH(Ti(OC4H9-)s) as the catalyst Eighty-four grams. 0.2mol). of p,p.'-sulfonyl dibenzoic acid butyl ester and 36 g. (0.3 mol)of 1,6-hexanediol were placed in a vessel equipped. with a variablespeed stirrer of the anchor type, a short distillation column, and a gasinlet tube for purified hydrogen. Two cc. of n-butyl alcohol containing0.1 g. of. NaH(Ti(OC4H9)s) were added. The mixture was heated in a metalbath at 200-210 and stirred at 100-200 R. P. M. while pure hydrogen waspassed over the surface Butyl alcohol distilled rapidly and the esterinterchange was practically complete in 30 minutes. The temperature wasthen raised to 270-280 C. in 15 minutes and. heating was continued for-15 minutes. Some of the excess glycol distilled off at this stage. Thehydrogen gas was shut off, and a vacuum of about 1 mm. of Hgpressure wasapplied. The melt rapidly increased in viscosity and in about minutes itwas necessary to reduce the stirrer speed to 40 R. P. M. As theviscosityincreased, the stirrer speed was gradually reduced. After a total timeof 30-40 minutes under vacuum, the melt had become too viscous to stirand the reaction was stopped. The melt obtained was clear and colorless.After cooling slowly, the product obtained was hard. and opaque, due tocrystallinity. If the melt is suddenly cooled or quenched, it has atendency to remain amorphous and transparent. On a hot stage, inpolarized light, the crystalline material shows a melting point of270-280 C. The inherent viscosity in 60% phenol-40% tetrachlorethane is0.70-0.80. Fibers can be pulled from the melt and cold-drawn 500-600 percent. They stick on a hot bar at230-240 C. The polyester also givesvaluable sheets and. films.

Example 2.LiH(Ti(OC2H5)s) as the catalyst One hundred gramsp,p'-sulfonyl dibenzoic acid ethyl ester and 40 g. 1,5-pentanediol wereplaced in a reaction vessel equipped with a stirrer, a shortdistillation column, and an inlet tube for purified nitrogen. Five cc.of ethyl alcohol containing 0.4 g. LiH(Ti(OC2H5)s) was added and themixture heated at 180-200" C. with stirring. After 1 hour, thedistillation of ethyl alcohol ceased, and the temperature was raised to280-285 C. where it was held for minutes. A vacuum of 0.5 to 1.0 mm. wasapplied for 1 hour, while the temperature was maintained at 280-285 C. Acolorless product having an inherent viscosity of 0.80-0.90 in 60%phenol-40% tetrachlorethane' solution was obtained. Fibers pulled fromthe melt and cold drawn 400-500 percentshow a sticking temperature of240-250 C. The product is also useful for films and sheets.

Example 3.-K2(Ti(OC2H5)s) as the catalyst One mol of methyl sebacate, 4mols of p,p-sulfonyl dibenzoic acid, butyl ester, and 7 mols1,6-hexanediol were placed in a vessel as described in Example 2.Fivehundredths. percent K2(Ti(OCzH5)s) was added, based on the weight ofthe two esters. A heating schedule similar to that given in Example 2'was followed. The product obtained is very tough and rubbery. It has aninherent viscosity of 0480 in a solvent of 60% phenol40%tetrachlorethanet Fibers pulled from the melt show a rubbery elasticelongation of 30-40 percent. This product isalso useful as a moldingplastic.

Example 4.-Li1(Ti( iso C4H90)e) as the catalyst One mol of methylisophthalate, 5 mols of p,p'-sulfonyl dibenzoic acid ethyl ester, and 10mols 1,5-pentanediol were placed in a vessel as described in Example 2.Sixhundredths percent Li2(Ti(O iso-C4I-I9) was added, based on theweight of the two esters. A heating schedule similar to thatgiven inExample 2 was followed. The product obtained is hard and crystalline. Itis useful for injection molding.

10 Example 5.--KH(Ti(OCH3)s) as the catalyst One hundred grams methylterephthalate and 40 g. ethylene glycol were placed in a vessel asdescribed in Example l. Three-hundredths percent KI-I(Ti(OCH3)s) wasadded, based on the weight of methyl terephthalate. A heating schedulewas followed as described in Example 1. A polyester having excellentcolor and an inherent viscosity of 0.80-0.90 was obtained.

Example 6.--Naz(Ti(OC4I-I9)s) as the catalyst Twenty grams diethyleneglycol and 42 g. p,p-sulfonyldibenzoic acid dibutyl ester were mixed ina vessel equipped with a stirrer. 0.1 gram of Na(Ti(OC4H9)s) was addedas a catalyst and the mixture stirred at 200- 210 C. until the evolutionof butyl alcohol practically stopped. Nine grams glycerine and 20 g.maleic anhydride were added, and heating was continued for minutes. Theproduct obtained is soluble in dioxane. With benzoyl peroxide catalyst,or with manganese and cobalt salts, it bakes to hard, insoluble films at-150" C.

Example 7.Naz(Ti(OC4H9)s) as the catalyst Three hundred and seventy-twog. (1.0 mol) of p,p'-sulfonyldibenzoic acid diethyl ester, 300 g. (1.5mol) dimethyl terephthalate, and 450 g. (5.0 mols) tetramethylene glycolwere placed in a reaction vessel equipped with a stirrer, a shortdistillation column, and aninlet for purified nitrogen. A solution of0.5 g. of sodium titanium butoxide in 10 cc. butyl alcohol was added asa catalyst. The mixture was stirred at 190-200 C. in a stream of purenitrogen. The distillation of methyl and butyl alcohols was 80-90%complete in two hours. The tem perature was raised to 265-270 and heldfor 40 minutes. A vacuum of 2 mm. was applied for 1.0 to 1.5 hours. Theproduct obtained has an inherent viscosity of 0.7 in 40%tetrachlorethane-60% phenol. It is soluble in 'y-butyrolactone, ethylenecarbonate, and sulfolane at l20l40 C. and precipitates when thesolutions are cooled. This polyester is especially valuable as aphotographic film base. It softens over the range of 210" C. and can beextruded readily by ordinary equipment to give films, sheets, rods,tubes, etc.

Example 8.-Na2(Ti(OC4H9)s) as the catalyst Four hundred and twenty grams(1.0 mole) of p,p-sulfonyldibenzoic acid dibutyl ester, grams (1.0 mole)of a,a-dimethyl glutaric acid dimethyl ester, and 360 g. (4.0 mole) oftetramethylene glycol were placed in a reaction vessel equipped with astirrer, a short distillation column, and an inlet for purifiedhydrogen. Ten cc. of butyl alcohol containing 0.25 g. of sodium titaniumbutoxide was added as catalyst and the mixture heated at 200- 210 C.with stirring. After one or two hours, the evolution of butyl and ethylalcohols practically ceased, showing that the ester interchange wascomplete. The temperature was then raised to 260-270 and held for 20-30minutes. A vacuum of 0.5 to 1.0 mm. was applied while the heating andstirring were continued for 2.5 to 3 hours. A colorless product having.an inherent viscosity of 0.7 to 0.8 in 60% phenol-40%tetrachlorethanewas obtained. This material begins to flow under pressure at about 180C. and gradually becomes softer as the temperature is raised. It doesnot have a sharp melting point. Because of its relatively wide softeningrange, the polyester is especially suitable for injection molding orextrusion. It can also be converted into films or sheets by extrusionthrough suitable dies. Films or fibers that have been oriented bydrafting and then heat treated show a hot bar sticking temperature of200-210" C. The polyester is soluble in hot gamma-butyrolactone, phenol,and tetrachlorethane. Molded or extruded objects made from the polymertend to be somewhat flexible and rubbery.

1 1 Example 9.Na2 (Ti(OC4H9)e) as the catalyst Four hundred and twentygrams (1.0 mole) p,p-sul- 'fonyl dibenzoic acid dibutyl ester, 300 g.(1.6 mole) (1,06- dimethyl glutaric acid dimethyl ester, and 360g.ethylene glycol were placed in a reaction vessel equipped with astirrer, a short distillation column, and an inlet for purifiednitrogen. A solution of 0.3 g. sodium titanium butoxide in cc. butylalcohol was added as catalyst. The mixture was stirred at 180190 C. in astream of nitrogen. A mixture of butyl and methyl alcohols distilled.The ester interchange was essentially complete in 2 hours. Thetemperature was then raised to 270275 C. and held for 30 minutes. Avacuum of 1.0 to 2.0 mm. was applied, while stirring was continued for 1to 1.5 hours. The product obtained has an inherent viscosity of 0.6 to0.70 in 60 phenol-40 tetrachlorethane. This product shows good flowcharacteristics when molded by injection methods. Films can be cast fromtetrachlorethane solutions. They can be used as photographic film basematerials.

Example 10.-Naz (Ti( OCzHs) s) as the catalyst Three hundred andseventy-two grams (1.0 mole) of p,p-sulfonyldibenzoic acid diethylester, 35 g. (0.3 mole) ethyl'carbonate, and 240 g. hexamethylene glycolwere placed in a reaction vessel equipped with a stirrer, a distillationcolumn, and an inlet for purified hydrogen. A solution of 0.3 g. sodiumtitanium ethoxide in ethyl alcohol was added as catalyst. The mixturewas heated at 100120 C. in a stream of pure hydrogen, with stirring.Ethyl alcohol distilled off from the reaction mix ture. The column wasadjusted so that no ethyl carbonate was removed. The temperature wasgradually raised to 200201 C. during a period of 4 hours. It was held atZOO-210 C. for 30 minutes, then raised to 260 C. and held for 30minutes. A vacuum of 2 to 3 mm. was then applied, and stirring wascontinued for 4 hours. A prodnot having an inherent viscosity of 0.60 to0.70 in 60% phenol-40% tetrachlorethane was obtained. The polyester canbe molded, extruded, or pressed to give shaped products. Films, afterorienting by drafting, followed by heat treatment, soften at 190200 C.This product is also useful as an electrical insulator. Octamethyleneglycol was used in place of the hexarnethylene glycol in this examplewhereby a product softening at 170-180 C. was obtained.

Example 1 1 .--Naz( Ti OC2H5 6) as the catalyst One hundred and eighteengrams (1.0 mole) of ethyl carbonate and 212 g. (2.0 moles)pentamethylene glycol were placed in a distilling flask equipped with afractionating column. A solution of 0.2 g. sodium titanium ethoxide inethanol was added as a catalyst and the mixture heated at 100120 C.Ethyl alcohol distilled, and the temperature was gradually raised to160170 C. When 1.7-1.9 moles of alcohol had been removed, the productwas cooled to room temperature. It consisted essentially of a lowmolecular weight pentamethylene carbonate polyester. The reactionproduct was placed in a vessel equipped with a stirrer, a shortdistillation column, and an inlet for purified hydrogen. Seven hundredand ten grams (1.7 moles) of p,p'-sulfonyldibenzoic acid dibutyl esterand 300 g. pentamethylene glycol were placed in the vessel. The mixturewas heated at ZOO-210 C. with stirring. After two hours, the evolutionof butyl alcohol ceased, showing that the ester interchange wasessentially complete. The temperature was then raised to 260265 C. andheld for thirty minutes. A vacuum of 0.5 to 1.0 mm. was applied, and thestirring continued at 260-265 C. for 2 hours. A light colored productwas obtained that has an inherent viscosity of 0.7 to 0.8 in 60%phenol-40% tetrachlorethane. The polyester begins to soften underpressure at 170180" C. It does not have a sharp melting point, butgradually softens over the temperature range of 170190 C. It can beinjection molded to give products that show ahighii'rnpact strength. Itis suitable for extrusion as rods, tubes, sheets, etc. The polyester issoluble in hot tetrachlorethane, and the solutions can be coated to givephotographic film base material.

Example 12.-Naz (Ti(OC4H9 6) as the catalyst Four hundred and twentygrams (1.0 mol) p,p-sulfonyldibenzoic acid dibutyl ester, 260 g. (1.5mol)' diethyl succinate, and 450 g. (5.0 mols) tetramethylene glycolwere placed in a reaction vessel equipped with a stirrer, a shortdistillation column, and an inlet tube for purified nitrogen. Ten cc. ofbutyl alcohol containing 0.25 g. sodium titanium butoxide was added as acatalyst, and the mixture was heated at 200-210 C. with stirring. Afterone or two hours, the evolution of ethyl and butyl alcohols ceased,showing that the ester interchange was practically complete. Thetemperature was then raised to 270-275 C. and held for 20-30 minutes. Avacuum of 0.5 to 1.0 mm. was applied, and the heating and stirring werecontinued for 2.5 to 3 hours. A colorless product having an inherentviscosity of 0.90 to 1.1 in 60% phenol-40% tetrachlorethane wasobtained. This polyester can be injection molded at about 250 C. to givecolorless products that are very tough and strong. They retain theirshape even when subjected to a temperature of 180-190 C. Rods, tubes,sheets, and profileshapes can be extruded by the usual methods. Thepolyester is especially suitable for conversion into fibers by meltspinning methods. After drafting and heat-treating, the fibers have astrength of 3.0 grams per denier and a reversible elongation of 2025%.They are valuable for the production of elastic garments.

Example 13.Liz(Ti(OC4H9)s) as the catalyst Four hundred and twenty grams(1.0 mol) p,p'sulfonyldibenzoic acid dibutyl ester, 366 g. (1.5 mol)ethyl azelate, and 330 g. butanediol-1,4 were placed in a reactionvessel as described in Example 1. A solution of 0.2 g. lithium titaniumbutoxide in 15 cc. butyl alcohol was added. The mixture was stirred at-200 C. in an atmosphere of purified nitrogen. A mixture of ethyl andbutyl alcohol distilled. The evolution of alcohol practically stoppedafter 2 hours, and the temperature was raised to 260-270 where it washeld for 30 minutes. A vacuum of 0.5 to 1.0 mm. was applied and thereaction mixture stirred at 260-270 for 3.5 to 5 hours. The product iscolorless and has an inherent viscosity of 0.85 in 60% phenol-40%tetrachlorethane. The polyester can be converted to films, tubes,sheets, rods, etc., by extrusion methods. Fibers can be made bymelt-spinning. The polymer is especially useful for injection molding.It is useful as an insulator for wire and other electrical equipment.

Example ]4.N32(Ti(OC4H9)6) as the catalyst Two hundred and twenty-twograms (1.4 mole) of diglycollic acid monohydrate and 450 g. (5 moles) oftetramethylene glycol were placed in a reaction vessel equipped with astirrer, a short distillation column,-and an inlet for purifiedhydrogen. The mixture was stirred at 200210 C. for 1.5 to 2 hours toconvert the acid to the glycol ester. Four hundred and twenty grams (1.0mole) of p,p-sulfonyldibenzoic acid dibutyl ester was added to thereaction vessel. A solution of 0.3 g. sodium titanium butoxide in 10 cc.butyl alcohol was added as catalyst. The mixture was stirred at 200210C. in a stream of hydrogen until the distillation of butyl alcoholpractically stopped, showing that the ester interchange was complete.The temperature was then raised to 260 C. and held for 30 minutes. Avacuum of 1.0 to 2.0 mm. was applied for 2 hours, while stirring wascontinued. A product having an inherent viscosity of 0.60 to 0.70 in 60%phenol-40% tetrachlorethane was o b tained. The polyester has arelatively wide softening drafting, and heat treating procedures.

13 range and can be injection molded at 180-200 C. to give productshaving a high impact strength. It is soluble in hot tetrachlorethane,phenol, and butyrolactone. It can be extruded to give rods, sheets,tubes, etc. It is useful as an electrical insulating material.

Example 15.Na2(Ti(OC4H9)6) as the catalyst Four hundred and twenty g.(1.0 mol) of p,p-sulfonyldibenzoic acid dibutyl ester, 106 g. (1.0 mol)diethylene glycol, and 104 g. (1.0 mol) pentamethylene glycol wereplaced in a reaction vessel as described in Example 1. A solution of 0.4g. sodium titanium butoxide in butyl alcohol was added as the catalyst.The mixture was stirred at 200-220 C. in pure nitrogen until about 80%of the butyl alcohol was distilled. The temperature was then raised to260 C. and held for 30 minutes. A vacuum of 1.0 to 2.0 mm. was appliedfor two hours while the stirring was continued. The product obtained hasa strong tendency to crystallize. It melts at 240-250 C. when in thecrystalline form. This polyester is especially valuable for theproduction of strong, elastic fibers by the melt spinning process. Afterdrawing and heat treating the fibers stick to the hot bar at 210-220 C.The polymer is also suitable for the manufacture of photographic filmbase.

Example 16.-Na2(Ti(OC4H9)e) as the catalyst Three hundred andseventy-two g. (1.0 mol) of p,psulfonyldibenzoic acid diethyl ester, 50g. (0.25 mol) dimethyl isophthalate, and 2 10 g. pentamethylene glycolwere placed in a reaction vessel as described in Example 1. A solutionof 0.3 g. sodium titanium butoxide in 10 cc. butyl alcohol was added asthe catalyst. The mixture was stirred at 210-215 C. in a stream ofpurified nitrogen until about 80-85% of the methyl and ethyl alcoholshad distilled. The temperature was then raised to 250-260 and held for30 minutes. A vacuum of 2 to 3 was applied for 2.5 hours. The productobtained is especially useful for the manufacture of photographic filmbase. When properly oriented and heat treated, it sticks to the hot barat about 200 C.

When 0.33 mol of dimethyl isophthalate is used in the above example, theproduct obtained sticks to the hot bar at 160-170.

Example 1 7.Na2(Ti(OC4H9)s) as the catalyst Three hundred andseventy-two grams (1.0 mole) of p,p-sulfonyldibenzoic acid diethyl esterand 160 g. (1.5 mole) hexamethylene glycol were placed in a reactionvessel equipped with a short distillation, a stirrer, and an inlet forpurified nitrogen. A solution of 0.2 g. sod'iurn titanium butoxide incc. butyl alcohol was added as the catalyst. The reaction mixture wasstirred at 210-220 C. in a stream of pure nitrogen until thedistillation of ethyl alcohol was 80-90% complete. The temperature wasthen raised to 275-280 and maintained for 1 hour. A vacuum of 1.0 to 2.0mm. was applied, while stirring was continued for 1 to 1.5 hours. Theproduct obtained has an inherent viscosity of 0460 to 0.70 in 40%tetrachlorethane-40% phenol mixture. This polymer is especially valuablefor the production of textile fibers. In the crystalline form, .it meltsat 270-280 C. When extruded as fibers and drafted, it sticks to the hotbar at 230-240 C. Fibers having an elongation of 20-25% and tensilestrength of 4 to 5 grams per denier can be obtained by suitablespinning, The polymer is soluble in 'y-butyrolactone, ethylenecarbonate, and dimethyl sulfolane at 140-160 C. It precipitates when thesolution is cooled.

Example 18.-Mg(Ti(OC4H9)s) as the catalyst Eighty-four grams (0.2 mol)of p,p'-sulfonyldibenzoic acid butyl ester and 36 g. (0.3 mol) of1,6-hexanediol were placed in a vessel equipped with a variable speedstirrer of the anchor type, a short distillation column,

and a gas inlet tube for purified hydrogen. Two cc. of n-butyl alcoholcontaining 0.1 g. of Mg(Ti(OC4H9)s) was added. The mixture was heated ina metal bath at 200-210 C. and stirred at -120 R. l. M. while purehydrogen was passed over the surface. Butyl alcohol distilled rapidlyand the ester-interchange was practically complete in 30 minutes. Thetemperature was then raised to 270-280 C. in 15 minutes and heatingcontinued for 10-15 minutes. Some of the excess glycol distilled at thisstage. The hydrogen gas was shut off, and a vacuum of about 1 mm.applied. The melt rapidly increases in viscosity and in about 15 minutesit was necessary to reduce the stirrer speed to 40 R. P. M. As theviscosity increased, the stirrer speed was gradually reduced. After atotal time of 30-40 minutes under vacuum, the melt had become tooviscous to stir and the reaction was stopped. The melt was clear andcolorless. After cooling slowly, the product obtained was hard andopaque, due to crystallinity. If the melt is suddenly cooled orquenched, it has a tendency to remain amorphous and transparent. On ahot stage, in polarized light, the crystalline material shows a meltingpoint of 270-280 C. The inherent viscosity in 60% phenol-40%tetrachlorethane is 0.70-0.80. Fibers can be pulled from the melt andcold drawn 500-600 per cent. They stick on a hot bar at 250-240 C. Thepolyester also gives valuable sheets and films.

Example 19.Mg(HTi(OC2I-I5)s)2 as the catalyst One hundred gramsp,p"-sulfonyldibenzoic acid ethyl ester and 40 g. 1,5-pentanediol wereplaced in a reaction vessel equipped with a stirrer, a shortdistillation column, and an inlet tube for purified nitrogen. Five cc.of ethyl alcohol containing 0.4 g. Mg(HTi( OCzH5)s)2 was added and themixture heated at -200 C. with stirring. After 1 hour, the distillationof ethyl alcohol ceased, and the temperature was raised to 280-285 C.where it was held for 20 minutes. A vacuum of 0.5 to 1.0 mm. was appliedfor 1 hour, while the temperature was maintained at 280-285 C. Acolorless product having an inherent viscosity of 0.80-0.90 in 60%phenol-40% tetrachlorethane solution was obtained. Fibers pulled fromthe melt and cold drawn 400-500 per cent show a sticking temperature of240-250 C. The product is also useful for films and sheets.

Example 20.Ca(Ti(OC2H5)s)2 as the catalyst One mol of methyl sebacate, 4mols of p,p-sulfonyldibenzoic acid, butyl ester, and 7 mols1,6-hexanedio1 were placed in a vessel as described in Example 19.Fivehundredths per cent Ca(Ti(OC2H5)e)2 was added, based on the weightof the two esters. A heating schedule similar to that given in Example19 was: followed. The product obtained was very tough and rubbery. Ithas an inherent viscosity of 0.80 in a solvent of 60% phenol- 40%tetrachlorethane. Fibers pulled from the melt show a rubbery elasticelongation of 30-40 per cent. This product is also useful as a moldingplastic.

Example 21.-Sr(HTi(OC4H9)s-)2 as the catalyst One mol of methylisopht-halate, 5 mols of p,p-sulfonyldibenzoic acid ethyl ester, and 10mols 1,5-pentanediol were placed in a vessel as described in Example 19.Six-hundredths per cent Sr('HTi(OC4H9)s)2 was added, based on the weightof the two esters. A heating schedule similar to that given in Example19 was followed. The product obtained 'was hard and crystalline. It isuseful for injection molding.

Example 22.-Mg(HTi(OCH3)s)2 as the catalyst One hundred grams methylterephthalate and 40 g. ethylene glycol were placed in a vessel asdescribed in Example 18. Three-hundredths per cent was added, based onthe weight of methyl terephthalate. A heating schedule was followed asdescribed in Ex- 15 ample 18. A polyester having excellent color and aninherent viscosity of 0.800.90 was obtained.

Example 23.Mg(HTi(OCeH13)e) as the catalyst One hundred grams of methylterephthalate and 40 grams of ethylene glycol were condensed asdescribed in Example 22 except that 0.03% of Mg(HTi(OCsH1s)e) wasemployed as the catalyst. A polyester having excellent color andviscosity was obtained.

Example 24.NaH (Ti OC4H9 s) as the catalyst One gram mole ofp,p-dicarbethoxydiphenyl methane and 2 gram moles of ethylene glycolwere condensed in apparatus as described in Example 1 according to theprocedure set forth therein employing 0.1 gram of the same catalyst. Theproduct obtained was a useful highly polymeric linear polyester usefulin preparing molding resins, films, sheets, etc.

Example 25.NaH(Ti(OC2H5)s) as the catalyst One gram mol ofp,p-dicarbomethoxybenzophenone and 2.2 gram moles of tetramethyleneglycol were condensed in apparatus as described in Example 1 accordingto the procedure set forth therein employing 0.1 gram of the samecatalyst. The product obtained was a highly polymeric linear polyesteruseful in preparing molding resins, films, sheets, etc.

gne gramsmole of 1,2-bis(p-carbopropoxyphenyloxy) ethane and 2.5 grammoles of ethylene glycol were conwherein R1 and R4 each represents asubstituent selected from the group consisting of an alkyl radicalcontaining from 1 to 10 carbon atoms and an omega-hydroxyalkyl radicalcontaining from 2 to 12 carbon atoms, R2 and R3 each represents (CH2)n 1wherein n is a positive integer of from 1 to inclusive, and X representsa divalent aromatic radical selected from the group consisting of thosehaving the following formulas:

wherein Y represents a divalent radical selected from the groupconsisting of and wherein m is a positive integer of from 1 to 5inclusive, (B) with an alpha, omega-dioxy compound comprising a compoundselected from the group consisting of those compounds having thefollowing formulas:

wherein p represents a positive integer of from 2 to 12 inclusive, R5and Rs each represents a substituent selected from the group consistingof a hydrogen atom and an acyl radical containing from 2 to 4 carbonatoms, R7 represents an alkylene radical containing from 2 to 4 carbonatoms and q represents a positive integer of from 1 to 10 inclusive, thealpha, omega-dioxy compound being employed in such a proportion thatthere is at least an equivalent amount of alpha and omega oxysubstituents in proportion to the carbalkoxy substituents in the overallcombination of the aromatic diester and the alpha, omegadioxy compound,(C) in the presence of a catalytic condensing agent selected from thegroup consisting of compounds having the following formulas:

MH(Ti(OR)s) M2(Ti(OR)6) M'(HTi(OR)6)2 and M (Ti (OR) 6) wherein Mrepresents an alkali metal, M represents an alkaline earth metalselected from the group consisting of magnesium, calcium and strontium,and R represents an alkyl group containing from 1 to 6 carbon atoms, (D)at an elevated temperature which is increased gradually during thecourse of the condensation up to a temperature of from about 225 toabout 310 C., (E) the condensation being conducted in an inertatmosphere, (F) and conducting the condensation at a very low pressureof the inert atmosphere during the latter part of the condensation.

2. A process as defined in claim 1 wherein the condensing agent isemployed in an amount of from about 0.005% to about 0.2% based on theweight of the aromatic dicarboxylic acid diester.

3. A process as defined in claim 2 wherein the alpha, omega-dioxycompound is employed in such a proportion that there are from about 1.2to about 3 alpha and omega oxy substituents in proportion to thecarbalkoxy substituents in the overall combination of the aromaticdiester and the alpha, omega-dioxy compound.

4. A process as defined in claim 3 wherein the elevated temperatureemployed during the earlier part of the condensation is from about C. toabout 220 C.

5. A process as defined in claim 4 wherein the low pressure definedunder (F) is less than 15mm of Hg pressure.

6. A process as defined in claim 5 wherein the low pressure definedunder (F) is less than 5mm of Hg pressure.

7. A process as defined in claim 6 wherein the aromatic diester isderived from p,p'-sulfonyl dibenzoic acid and the condensing agent isNaH(Ti(OC4I-Is)s).

8. A process as defined in claim 6 wherein the aromatic diester isderived from p,p-sulfonyl dibenzoic acid and the condensing agent is Mg(HTi(OC2H5)e)2.

9. A process as defined in claim 6 wherein the aromatic diester isderived from p,p'-sulfonyl dibenzoic acid and the condensing agent isLiH(Ti(OC2H5)s).

10. A process as defined in claim 6 wherein the aromatic diester isderived from terephthalic acid and the condensing agent is KH(Ti(OCHs e)11. A process as defined in claim 6 wherein the aro- 17 matic diester isderived from terephthalic acid and the condensing agent isNaH(Ti(OC4Hs)s).

12. A process as defined in claim 1 wherein the aromatic dicarboxylicacid diester is formed by a preliminary step comprising condensing anaromatic dicarboxylic acid having the formula:

wherein R2, R and X are defined under (A), With an alpha, omega-dioxycompound which is defined under (B) and is employed in the proportionsset forth under (B), atan elevated temperature, after which preliminarystep the catalytic condensing agent which is defined under (C) is addedand the condensation is completed as defined under (D), (E) and (F).

13. A process as defined in claim 12 wherein the elevated temperatureemployed during the preliminary step is substantially that at whichreflux conditions subsist, and the condensing agent is employed in anamount of from about 0.005% to about 0.2% based on the weight of thearomatic dicarboxylic acid diester, the alpha, omega-dioxy compound isemployed in such a proportion that there are from about 1.2 to about 3alpha and omega oxy substituents in proportion to the acid substituentsin the overall combination of the aromatic diester and the alpha,omega-dioxy compound, the elevated temperature employed during theearlier part of the condensation to form the polyester is from about 150C.. to about 220 C., the low pressure defined under (F) is less thanabout 15 mm. of Hg pressure and all materials employed in the processare substantially anhydrous.

References Cited in the file of this patent Meerwein et al.: Ann., vol.476, pages 113-150 (1929); vol. 455, 227 (1927).

1. A PROCESS FOR PREPARING A POLYESTER COMPRISING (A) CONDENSING UNDERSUBSTANTIALLY ANHYDROUS CONDITIONS AN AROMATIC DICARBOXYLIC ACID DIESTERHAVING THE FORMULA: